Scalar resonance contributions to the dipion transition rates of Y(4S,5S) in the rescattering model

In order to explain the observed unusually large dipion transition rates of Y(10870), the scalar resonance contributions in the rescattering model to the dipion transitions of Y(4S) and Y(5S) are studied. Since the imaginary part of the rescattering amplitude is expected to be dominant, the large ratios of the transition rates of Y(10870), which is identified with Y(5S), to that of Y(4S) can be understood as mainly coming from the difference between the p values in their decays into open bottom channels, and the ratios are estimated numerically to be about 200-600 with reasonable choices of parameters. The absolute and relative rates of Y(5S)-> Y(1S,2S,3S)pi(+)pi(-) and Y(5S)-> Y(1S)K+K- are roughly consistent with data. We emphasize that the dipion transitions observed for some of the newly discovered Y states associated with charmonia may have similar features to the dipion transitions of Y(5S). Measurements on the dipion transitions of Y(6S) could provide further tests for this mechanism.